Additive effect of coexistent type 2 diabetes and arterial hypertension on endothelial dysfunction in resistance arteries of human forearm vasculature

Vascular nitric oxide resistance in type 2 diabetes

Vascular nitric oxide (NO•) resistance, manifested by an impaired vasodilator function of NO• in both the macro- and microvessels, is a common state in type 2 diabetes (T2D) associated with developing cardiovascular events and death. Here, we summarize experimental and human evidence of vascular NO• resistance in T2D and discuss its underlying mechanisms. Human studies indicate a ~ 13-94% decrease in the endothelium (ET)-dependent vascular smooth muscle (VSM) relaxation and a 6-42% reduced response to NO• donors, i.e., sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), in patients with T2D. A decreased vascular NO• production, NO• inactivation, and impaired responsiveness of VSM to NO• [occurred due to quenching NO• activity, desensitization of its receptor soluble guanylate cyclase (sGC), and/or impairment of its downstream pathway, cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)] are the known mechanisms underlying the vascular NO• resistance in T2D. Hyperglycemia-induced overproduction of reactive oxygen species (ROS) and vascular insulin resistance are key players in this state. Therefore, upregulating vascular NO• availability, re-sensitizing or bypassing the non-responsive pathways to NO•, and targeting key vascular sources of ROS production may be clinically relevant pharmacological approaches to circumvent T2D-induced vascular NO• resistance.

Endothelial function and arterial stiffness indexes in subjects with carotid plaque and carotid plaque length: A subgroup analysis showing the relationship with hypertension and diabetes

BACKGROUND

Stroke is a leading cause of death and disability globally. A large proportion of ischemic strokes are caused by carotid atherosclerotic plaques. However, the relationship between vascular health status (arterial stiffness and endothelial dysfunction) and carotid plaque remains unclear.

OUR STRATEGY

Here, we recruited 991 subjects with carotid plaques and 1170 subjects without carotid plaques to measure arterial stiffness and endothelial dysfunction, using a logistic regression model and multiple linear regression models to predict the relationship between them and carotid plaques.

MAIN RESULTS

The data revealed that patients with carotid plaques presented a significantly higher mean of cf-PWV and lower mean RHI values. Age, male gender, diabetes, hypertension, and smoking contributed to plaque formation. Carotid plaques and their lengths were negatively associated with RHI values and positively associated with cf-PWV values; diabetes combined with hypertension showed a cumulative effect on arteriosclerosis.

CONCLUSION

RHI combined with cf-PWV could improve the efficacy of predicting the presence of carotid plaques and their lengths.

GLP-1 and insulin regulation of skeletal and cardiac muscle microvascular perfusion in type 2 diabetes

Muscle microvasculature critically regulates skeletal and cardiac muscle health and function. It provides endothelial surface area for substrate exchange between the plasma compartment and the muscle interstitium. Insulin fine-tunes muscle microvascular perfusion to regulate its own action in muscle and oxygen and nutrient supplies to muscle. Specifically, insulin increases muscle microvascular perfusion, which results in increased delivery of insulin to the capillaries that bathe the muscle cells and then facilitate its own transendothelial transport to reach the muscle interstitium. In type 2 diabetes, muscle microvascular responses to insulin are blunted and there is capillary rarefaction. Both loss of capillary density and decreased insulin-mediated capillary recruitment contribute to a decreased endothelial surface area available for substrate exchange. Vasculature expresses abundant glucagon-like peptide 1 (GLP-1) receptors. GLP-1, in addition to its well-characterized glycemic actions, improves endothelial function, increases muscle microvascular perfusion, and stimulates angiogenesis. Importantly, these actions are preserved in the insulin resistant states. Thus, treatment of insulin resistant patients with GLP-1 receptor agonists may improve skeletal and cardiac muscle microvascular perfusion and increase muscle capillarization, leading to improved delivery of oxygen, nutrients, and hormones such as insulin to the myocytes. These actions of GLP-1 impact skeletal and cardiac muscle function and systems biology such as functional exercise capacity. Preclinical studies and clinical trials involving the use of GLP-1 receptor agonists have shown salutary cardiovascular effects and improved cardiovascular outcomes in type 2 diabetes mellitus. Future studies should further examine the different roles of GLP-1 in cardiac as well as skeletal muscle function.

The continuums of impairment in vascular reactivity across the spectrum of cardiometabolic health: A systematic review and network meta-analysis

This study aimed to assess, for the first time, the change in vascular reactivity across the full spectrum of cardiometabolic health. Systematic searches were conducted in MEDLINE and EMBASE databases from their inception to March 13, 2017, including studies that assessed basal vascular reactivity in two or more of the following health groups (aged ≥18 years old): healthy, overweight, obesity, impaired glucose tolerance, metabolic syndrome, or type 2 diabetes with or without complications. Direct and indirect comparisons of vascular reactivity were combined using a network meta-analysis. Comparing data from 193 articles (7226 healthy subjects and 19344 patients), the network meta-analyses revealed a progressive impairment in vascular reactivity (flow-mediated dilation data) from the clinical onset of an overweight status (-0.41%, 95% CI, -0.98 to 0.15) through to the development of vascular complications in those with type 2 diabetes (-4.26%, 95% CI, -4.97 to -3.54). Meta-regressions revealed that for every 1 mmol/l increase in fasting blood glucose concentration, flow-mediated dilation decreased by 0.52%. Acknowledging that the time course of disease may vary between patients, this study demonstrates multiple continuums of vascular dysfunction where the severity of impairment in vascular reactivity progressively increases throughout the pathogenesis of obesity and/or insulin resistance, providing information that is important to enhancing the timing and effectiveness of strategies that aim to improve cardiovascular outcomes.

Statin therapy increases vascular sensitivity to angiotensin II in hypercholesterolaemic patients

Introduction Cross-talk between various cardiovascular risk factors has been suggested by a number of studies. This study examines the interaction between hypercholesterolaemia and the renin-angiotensin system in vivo in man.

Methods We performed a randomised, placebo-controlled, double-blind crossover study on 40 hypercholesterolaemic patients, comparing cholesterol-lowering therapy with a statin for six months versus placebo. Brachial artery function was assessed by bilateral venous occlusion plethysmography using intra-arterial infusions of the endothelial-dependent vasoconstrictors, angiotensin I (Ang I) and angiotensin II (Ang II), to measure vascular angiotensin-converting enzyme (ACE) and Ang II receptor response respectively. The endothelial-independent vasoconstrictor, noradrenaline, was used as a control vasoconstrictor. Results were analysed by multiple analysis of variance and statistical significance

Cholesterol-lowering treatment with a statin was taken as a p value <0.05. Results Cholesterol-lowering treatment with alstatin significantly reduced the mean total cholesterol level to 5.71 mmol/L vs. 7.57 mmol/L on placebo (p<0.0001). Hypercholesterolaemia significantly increased the vasoconstriction response to noradrenaline (placebo versus statin treatment; p=0.046). In hypercholesterolaemia, there was a strong trend towards a reduction in the vasoconstriction response to Ang I (placebo versus statin treatment; p=0.089). In hypercholesterolaemia, the vasoconstriction response to Ang II was significantly reduced (placebo versus statin treatment; p=0.01).

Conclusions Our in vivo results show that, unlike some other previous work, hypercholesterolaemia is associated with down-regulation of the vasoconstrictor response to Ang II and that statin therapy up-regulates the local vasoconstrictor response to Ang II. The possibility now arises that, in man, statins alter the balance between AT1-receptors and AT2-receptors.

Vascular function, insulin action, and exercise: an intricate interplay

Insulin enhances the compliance of conduit arteries, relaxes resistance arterioles to increase tissue blood flow, and dilates precapillary arterioles to expand muscle microvascular blood volume. These actions are impaired in the insulin resistant states. Exercise ameliorates endothelial dysfunction and improves insulin responses in insulin resistant patients, but the precise underlying mechanisms remain unclear. The microvasculature critically regulates insulin action in muscle by modulating insulin delivery to the capillaries nurturing the myocytes and trans-endothelial insulin transport. Recent data suggest that exercise may exert its insulin-sensitizing effect via recruiting muscle microvasculature to increase insulin delivery to and action in muscle. The current review focuses on how the interplay among exercise, insulin action, and the vasculature contributes to exercise-mediated insulin sensitization in muscle.

Hypertension in obese type 2 diabetes patients is associated with increases in insulin resistance and IL-6 cytokine levels: potential targets for an efficient preventive intervention

Increased body weight as well as type 2 diabetes (T2D) are found to be associated with increased incidence of hypertension, although the mechanisms facilitating hypertension in T2D or nondiabetic individuals are not clear. Therefore, in this study we compared the levels of insulin resistance (IR:OGIS), plasma insulin (PI:RIA) levels, and pro-inflammatory cytokines (IL-6 and TNF-α: ELISA), being risk factors previously found to be associated with hypertension, in T2D patients showing increased body weight (obese and overweight, BMI ≥ 25 kg/m²) with hypertension (group A, N = 30), or without hypertension (group B, N = 30), and in nonobese (BMI < 25 kg/m²), normotensive controls (group C, N = 15). We found that OGIS index was the lowest (A: 267 ± 35.42 vs. B: 342.89 ± 32.0, p < 0.01) and PI levels were the highest (A: 31.05 ± 8.24 vs. B: 17.23 ± 3.23, p < 0.01) in group A. In addition, IL-6 levels were higher in group A (A: 15.46 ± 5.15 vs. B: 11.77 ± 6.09; p < 0.05) while there was no difference in TNF-α levels. Our results have shown that appearance of hypertension in T2D patients with increased body weight was dependent on further increase in IR which was associated with the rise in pro-inflammatory IL-6 cytokine. The results imply that lifestyle intervention aimed to decrease IR might be beneficial in reducing the risk for hypertension in those T2D individuals.

Prevalence and predictors of abnormal arterial function in statin-treated type 2 diabetes mellitus patients

Arterial dysfunction (AD) in type 2 diabetes mellitus (T2DM) predicts cardiovascular events. The objective was to investigate the prevalence and predictors of AD in statin-treated T2DM patients. We measured flow-mediated (FMD) and nitrate-mediated (NMD) brachial artery dilatation in 86 statin-treated T2DM patients. Patients were classified into 2 groups: normal arterial function (FMD ≥3.7% with NMD ≥11.9%) or AD (FMD <3.7% with or without NMD <11.9%). Endothelial dysfunction without smooth muscle cell dysfunction (ED) was defined as FMD less than 3.7% with NMD of at least 11.9%, and endothelial dysfunction with smooth muscle cell dysfunction (ED/SMD) was defined as FMD less than 3.7% with NMD less than 11.9%. Predictors of arterial function were investigated using linear and logistic regression methods. The prevalence of AD was 33.7% (23.2% with ED and 10.5% with ED/SMD). In multivariate linear regression, history of hypertension (P < .01), statin dose (P < .05), and estimated glomerular filtration rate (eGFR) (P = .02) were significant predictors of FMD. Sex (P < .01) and creatinine (P = .03) or eGFR (P = .02) predicted NMD. In multivariate logistic regression, the independent predictors of AD were history of hypertension (odds ratio [OR], 8.79; 95% confidence interval, 2.14-36.12; P < .01), age (OR, 1.08; 1.01-1.17; P = .03), and statin dose (OR, 0.33; 0.12-0.87; P = .02). A history of hypertension (OR, 8.99; 1.87-43.26; P < .01) was the sole independent predictor of ED; eGFR (OR, 0.01; 0.00-0.26; P < .01) independently predicted ED/SMD. Our data suggest that one third of statin-treated diabetic patients have residual AD, mainly due to ED alone. Earlier identification and treatment of hypertension and renal impairment may improve AD and further decrease cardiovascular risk in such patients.

Insulin regulates its own delivery to skeletal muscle by feed-forward actions on the vasculature

Insulin, at physiological concentrations, regulates the volume of microvasculature perfused within skeletal and cardiac muscle. It can also, by relaxing the larger resistance vessels, increase total muscle blood flow. Both of these effects require endothelial cell nitric oxide generation and smooth muscle cell relaxation, and each could increase delivery of insulin and nutrients to muscle. The capillary microvasculature possesses the greatest endothelial surface area of the body. Yet, whether insulin acts on the capillary endothelial cell is not known. Here, we review insulin's actions at each of three levels of the arterial vasculature as well as recent data suggesting that insulin can regulate a vesicular transport system within the endothelial cell. This latter action, if it occurs at the capillary level, could enhance insulin delivery to muscle interstitium and thereby complement insulin's actions on arteriolar endothelium to increase insulin delivery. We also review work that suggests that this action of insulin on vesicle transport depends on endothelial cell nitric oxide generation and that insulin's ability to regulate this vesicular transport system is impaired by inflammatory cytokines that provoke insulin resistance.

Effects of salbutamol and glyceryl trinitrate on large arterial stiffness are similar between patients with hypertension and adults with normal blood pressure

AIMS

Endothelial function is characteristically impaired in patients with hypertension. Endothelial function was assessed in men and women with hypertension using a recently described, non-invasive method.

METHODS

Twenty patients and 20 controls received salbutamol 400 microg and glyceryl trinitrate (GTN) 500 microg in a two-way randomized, single-blind study. Effects on augmentation index (AIx) were assessed using pulse wave analysis (PWA).

RESULTS

Responses (absolute AIx reduction and 95% confidence interval) to salbutamol were 8.4% (6.2, 10.6) and 8.3% (7.0, 9.6) in patients and controls, respectively, and those to GTN were 13.6% (10.8, 16.4) and 15.5% (13.0, 17.0), respectively.

CONCLUSIONS

Systemic arterial responses to endothelium-dependent and -independent vasodilators are preserved in patients with mild, uncomplicated hypertension, indicating normal large arterial endothelial function.

Systolic and diastolic hypertension impair endothelial vasodilatory function in different types of vessels in the elderly: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Endothelium-dependent vasodilation (EDV) is known to be impaired in middle-aged hypertensive individuals, but less is known regarding hypertension in the elderly.

OBJECTIVE

In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, different techniques to evaluate EDV in resistance and conduit arteries were applied in elderly subjects and were related to the type of hypertension.

DESIGN AND METHODS

In this population-based study, 1016 subjects aged 70 years were evaluated by the invasive forearm technique with acetylcholine (EDV), brachial artery ultrasound to assess flow-mediated dilatation (FMD) and pulse wave analysis with a beta-2 receptor agonist challenge, terbutaline. Those without antihypertensive treatment were divided into three groups: normotensive individuals (n = 256), and those with isolated systolic hypertension (n = 309) or combined systolic/diastolic hypertension (n = 79).

RESULTS

Compared with normotensive individuals, EDV was reduced in those with combined systolic/diastolic hypertension only (P = 0.0019), whereas FMD was mainly reduced in those with isolated systolic hypertension (P = 0.013). Furthermore, in regression analysis, EDV was related to diastolic blood pressure only (r = -0.10, P = 0.017), whereas FMD was mainly related to systolic blood pressure (r = -0.13, P = 0.0023). The pulse wave-based method to analyse vasoreactivity was not consistently affected by hypertension.

CONCLUSIONS

In elderly subjects, systolic hypertension mainly impairs conduit artery endothelial vasodilatory function, whereas diastolic hypertension mainly induces dysfunction in resistance arteries.

Clustering of insulin resistance with vascular dysfunction and low-grade inflammation in type 2 diabetes

Vascular dysfunction, low-grade inflammation, insulin resistance, and impaired fibrinolysis have each been reported to be present in type 2 diabetes, but their relationships, and the role of obesity, have not been investigated. We measured insulin sensitivity (euglycemic clamp), forearm blood flow responses to graded local acetylcholine (Ach) and sodium nitroprusside (SNP) infusions, plasma concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, von Willebrand factor (vWF), plasminogen activator inhibitor (PAI)-1, tissue plasminogen activator (tPA), and high-sensitivity C-reactive protein (hs-CRP) in 81 diabetic patients. When patients were stratified by insulin resistance, more severe insulin resistance was associated (P < 0.05) with overweight, central fat distribution, hypertension, and dyslipidemia (with similar sex distribution, age, fasting plasma glucose, and HbA1c). With regard to vascular function, both endothelium-dependent (Ach) (-22, -40, and -52%; P < 0.0001) and -independent (SNP) (-3, -7, and -27%; P < 0.02) vasodilatation were progressively reduced across insulin resistance tertiles. In multivariate analysis, inflammatory markers (IL-6, hs-CRP, and TNF-alpha) were independently associated with insulin resistance and fasting glycemia, fibrinolytic markers PAI-1 and tPA with insulin resistance and central fat distribution, and vascular indexes (vWF, Ach, and SNP vasodilation) with insulin resistance and obesity or cytokines (TNF-alpha or IL-6). In type 2 diabetes, insulin resistance is associated with vascular dysfunction/damage, impaired fibrinolysis, and low-grade inflammation independently of obesity and poor glycemic control.

Optimized Heart Failure Therapy and Complete Anemia Correction on Left-Ventricular Hypertrophy in Nondiabetic and Diabetic Patients Undergoing Hemodialysis

BACKGROUND

According to new guidelines, diabetes mellitus per se can be considered as stage I chronic heart failure (CHF). Available evidence suggests that patients suffering from both diabetes mellitus and renal insufficiency have disproportionately high rates of left-ventricular hypertrophy (LVH).

METHODS

Optimized heart failure therapy, including beta-blockers, ACE-inhibitors and AT II-type-1-receptor-blockers, was prescribed in combination with complete anemia correction using epoetin beta (target hemoglobin: 13.5 g/dl for women; 14.5 g/dl for men) to 230 patients (55% male) with ambulatory hemodialysis, including 60 patients (52% male) with diabetes. Echocardiographic follow-up examinations were performed over a mean period of 4.4 +/- 1.2 years.

RESULTS

Mean hemoglobin levels at the study end significantly increased to target levels in the entire study population and in patients with diabetes (both p < 0.001). Compared with baseline, significant improvements were seen in hemodialysis patients - both without and with diabetes - in left-ventricular mass index (-28.8 g/m2 [p < 0.001] and 29.0 g/m2 [p < 0.005], respectively), left-ventricular ejection fraction (+7.0% [p < 0.001] and +8.3% [p < 0.01], respectively) and in NYHA class (-0.84 [p < 0.01] and -1.12 [p < 0.01], respectively). Similar to the results in the overall population, a highly significant reduction in LVH (p < 0.005) and significant improvements in LVEF (p < 0.01) and NYHA class (p < 0.01) were seen in the high-risk subgroup of diabetic patients.

CONCLUSIONS

Patients undergoing hemodialysis, with or without concomitant diabetes, benefit considerably from optimized, multifactorial heart failure therapy combined with complete anemia correction.

Cardiovascular protection in patients with type 2 diabetes mellitus: Considerations about the tightness of blood pressure control and the choice of treatment

Diabetes mellitus is rapidly evolving as the epidemic of the 21st century. The presently estimated number of 190 million is predicted to grow to over 300 million by the year 2025. Cardiovascular (CVD) morbidity and mortality is two to five times higher in diabetics, while the microvascular complications considerably compromise the quality of life. The main risk factors for CVD, as well as for microangiopathy, are hypertension, dyslipidemia, insulin resistance, hyperglycemia, endothelial dysfunction, and an inflammatory vascular reaction. This review will focus on hypertension, which develops in most patients within the first 10-15 years of their diabetes. The discussion will encompass the criteria for treatment, the target values of blood pressure, and the choice of antihypertensive drugs as primary agents and in various combinations. The special role of angiotensin-receptor blockers will be highlighted, with an emphasis on cardioprotection, risk reduction of stroke, and attenuation of the course of nephropathy.

Coronary circulatory dysfunction in insulin resistance, impaired glucose tolerance, and type 2 diabetes mellitus

BACKGROUND

Abnormal coronary endothelial reactivity has been demonstrated in diabetes and is associated with an increased rate of cardiovascular events. Our objectives were to investigate the presence of functional coronary circulatory abnormalities over the full spectrum of insulin resistance and to determine whether these would differ in severity with more advanced states of insulin resistance.

METHODS AND RESULTS

Myocardial blood flow (MBF) was measured with positron emission tomography and 13N-ammonia to characterize coronary circulatory function in states of insulin resistance without carbohydrate intolerance (IR), impaired glucose tolerance (IGT), and normotensive and hypertensive type 2 diabetes mellitus (DM) compared with insulin-sensitive (IS) individuals. Indices of coronary function were total vasodilator capacity (mostly vascular smooth muscle-mediated) during pharmacological vasodilation and the nitric oxide-mediated, endothelium-dependent vasomotion in response to cold pressor testing. Total vasodilator capacity was similar in normoglycemic individuals (IS, IR, and IGT), whereas it was significantly decreased in normotensive (-17%) and hypertensive (-34%) DM patients. Compared with IS, endothelium-dependent coronary vasomotion was significantly diminished in IR (-56%), as well as in IGT and normotensive and hypertensive diabetic patients (-85%, -91%, and -120%, respectively).

CONCLUSIONS

Progressively worsening functional coronary circulatory abnormalities of nitric oxide-mediated, endothelium-dependent vasomotion occur with increasing severity of insulin-resistance and carbohydrate intolerance. Attenuated total vasodilator capacity accompanies the more clinically evident metabolic abnormalities in diabetes.

Vascular effects of improving metabolic control with metformin or rosiglitazone in type 2 diabetes

OBJECTIVE

The aim of this study was to test whether vascular reactivity is modified by improving metabolic control and peripheral insulin resistance in type 2 diabetes.

RESEARCH DESIGN AND METHODS

In a randomized, double-blind design, we assigned 74 type 2 diabetic patients to rosiglitazone (8 mg/day), metformin (1,500 mg/day), or placebo treatment for 16 weeks and measured insulin sensitivity (euglycemic insulin clamp), ambulatory blood pressure, and forearm blood flow response to 1) intra-arterial acetylcholine (ACh), 2) intra-arterial nitroprusside, 3) the clamp, and 4) blockade of nitric oxide (NO) synthase.

RESULTS

Compared with 25 nondiabetic subjects, patients had reduced insulin sensitivity (30 +/- 1 vs. 41 +/- 3 micromol. min(-1). kg fat-free mass(-1); P < 0.001) and reduced maximal response to ACh (586 +/- 42 vs. 883 +/- 81%; P < 0.001). Relative to placebo, 16 weeks of rosiglitazone and metformin similarly reduced fasting glucose (-2.3 +/- 0.5 and -2.3 +/- 0.5 mmol/l) and HbA(1c) (-1.2 +/- 0.3 and -1.6 +/- 0.3%). Insulin sensitivity increased with rosiglitazone (+6 +/- 3 micromol. min(-1). kg fat-free mass(-1); P < 0.01) but not with metformin or placebo. Ambulatory diastolic blood pressure fell consistently (-2 +/- 1 mmHg; P < 0.05) only in the rosiglitazone group. Nitroprusside dose response, clamp-induced vasodilatation, and NO blockade were not affected by either treatment. In contrast, the slope of the ACh dose response improved with rosiglitazone (+40% versus baseline, P < 0.05, +70% versus placebo, P < 0.005) but did not change with either metformin or placebo. This improvement in endothelium-dependent vasodilatation was accompanied by decrements in circulating levels of free fatty acids and tumor necrosis factor-alpha.

CONCLUSIONS

At equivalent glycemic control, rosiglitazone, but not metformin, improves endothelium dependent vasodilatation and insulin sensitivity in type 2 diabetes.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.

L-arginine-induced vasodilation of the renal vasculature is not altered in hypertensive patients with type 2 diabetes

OBJECTIVE

Diabetes, arterial hypertension, hypercholesterolemia, and aging are associated with endothelial dysfunction in various vasculatures. Endothelium-dependent vasodilation of the renal vasculature cannot be easily assessed, but infusion of L-arginine, the substrate of endothelial nitric oxide synthase, leads to an increase in renal plasma flow (RPF) in humans. We have examined the effect of L-arginine infusion on renal hemodynamics in hypertensive patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty-three elderly patients with type 2 diabetes (age, 65 +/- 6 years; HbA(1c), 7.8 +/- 1.6%) with coexisting arterial hypertension (158 +/- 19/83 +/- 11 mmHg) and elevated cholesterol levels (total cholesterol, 215 +/- 33 mg/dl) were examined. These patients were compared with a young and healthy reference group (n = 20; age, 26 +/- 2 years). The effect of L-arginine infusion (100 mg/kg over 30 min) on RPF and glomerular filtration rate were measured using the constant input clearance technique with p-aminohippurate and inulin, respectively.

RESULTS

L-arginine infusion similarly influenced renal hemodynamics in patients and reference subjects: RPF increased by 7 +/- 11 and 7 +/- 11% in diabetic and reference subjects, respectively (P = NS). Other parameters of renal hemodynamics such as glomerular filtration rate (5 +/- 5 vs. 4 +/- 4%) and filtration fraction (-1 +/- 8 vs. -1 +/- 9%) were not significantly different between diabetic and reference subjects, too.

CONCLUSIONS

L-arginine-induced vasodilation of the renal vasculature is not different between a group of hypertensive diabetic patients and a young, healthy reference group. These data were obtained using low-dose L-arginine infusion.

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.